A HVAC system typically has a fan to propagate an airflow to facilitate, for example, heat exchange between an interior and an exterior of the HVAC system. The fan, such as a plenum fan, typically has an air inlet and an air outlet. When the fan is in operation, air can be sucked into the inlet and dispersed by, for example, a centrifugal force generated by an impeller of the plenum fan.
Operation of the fan of the HVAC system can produce noise. Instabilities and/or turbulence (such as eddies) in an airflow sucked into the inlet of the fan may cause noise when the airflow interacts with the impeller of the fan. Multiple reasons can cause the instabilities and/or turbulence in the airflow moving toward the inlet. For example, when an air duct leading to the air inlet has a sharp turn positioned relatively close to the air inlet, the turn may generate instabilities and/or turbulence in the airflow moving toward the air inlet.